Gas-liquid viscosity measuring system suitable for helium and other low-temperature fluids

Abstract

The invention discloses a gas-liquid viscosity measuring system suitable for helium and other low-temperature fluids. The gas-liquid viscosity measuring system comprises a measuring unit, a low-temperature single temperature control unit and a signal acquisition unit, the measuring unit comprises a metal wire with two clamped ends and a permanent magnet; the signal acquisition unit measures the viscosity by measuring the weak induced electromotive force of the metal wire in the magnetic field; the low-temperature unit provides stable cooling capacity for the whole device through liquid nitrogen, and the temperature control unit can maintain the device in a temperature interval as low as 80K. The device is compact in structure and high in stability, and can realize high-precision viscosity test of gas-liquid fluid at low temperature.

Description

Technical Field

[0001] The invention belongs to the technical field of fluid thermal property measurement, and in particular relates to a gas-liquid viscosity measurement system suitable for helium and other cryogenic fluids. Background Art

[0002] Viscosity is a property that measures the friction between molecules when a fluid moves under the action of an external force. It is one of the important physical properties of a fluid. The measurement of viscosity is of great significance in fields such as petrochemicals and air separation. For example, in the separation and purification of natural gas, the temperature range of the cryogenic fluid mixture involved is as low as 80K. Obtaining the viscosity of these cryogenic fluids can provide an important reference for the design of process units such as distillation towers and separators. For another example, viscosity data can be used to verify the accurate calculation of the low-temperature density of helium fluids.

[0003] At present, the measurement methods of fluid viscosity include capillary method, falling ball method, rotation method, vibration method, etc. The capillary method is mainly used for measuring viscosity at normal pressure or saturated vapor pressure of fluid, but its system under high pressure conditions is relatively complex and the measurement accuracy is limited; the falling ball method is suitable for measuring the viscosity of fluids with higher viscosity, but the measurement accuracy is affected by the processing accuracy of the falling ball itself, and the measurement accuracy is difficult to guarantee; the rotation method has a wide range of applications, but it is easy to cause inner cylinder eccentricity and wall slippage of the measured fluid during measurement, which affects the measurement accuracy. In contrast, the vibrating string method has a sound theoretical basis, high measurement stability, and high measurement accuracy. However, when the measurement environment extends to the low temperature field, especially the liquid nitrogen temperature range close to 80K, a series of technical difficulties emerge. These difficulties include but are not limited to cabin sealing, management of thermal expansion and contraction effects of materials in low temperature environments, heat leakage control, temperature control requirements, and precise liquid level monitoring. These challenges not only require more sophisticated structural design, but also put forward more stringent standards for experimental operations. Not only will the repeatability and accuracy of low-temperature fluid viscosity measurement be reduced, but it may even make the measurement work completely impossible.

[0004] In view of this, the main purpose of the present invention is to establish a gas-liquid viscosity measurement system suitable for temperatures as low as liquid nitrogen. Summary of the invention

[0005] In view of the limitation of the prior art in measuring the viscosity of low-temperature fluids in the liquid nitrogen temperature zone, the present invention provides a gas-liquid viscosity measurement system as low as the liquid nitrogen temperature zone, which uses liquid nitrogen as the cold background and a helium layer as a cold quantity regulation layer, and indirectly obtains viscosity data by collecting the vibrating string voltage signal of the energized tungsten wire after being excited in the magnetic field.

[0006] The present invention is achieved through the following technical solutions:

[0007] A gas-liquid viscosity measurement system suitable for helium and other cryogenic fluids, characterized in that it includes:

[0008] A viscosity measuring unit, used for measuring the viscosity of a fluid, comprises an electrode pressing block, a metal wire, a permanent magnet, a magnet fixing member, a support rod and a clamping flange; wherein the electrode pressing block is used for pressing the two ends of the metal wire to ensure that the metal wire has a fixed length and a constant tension; the metal wire is located in the magnetic field generated by the permanent magnet as a vibrating element; the permanent magnet is used for generating a uniform magnetic field so that the metal wire generates an induced electromotive force when vibrating; the magnet fixing member is used for fixing the permanent magnet on both sides of the metal wire; the clamping flange is insulated from the electrode pressing block and is used for fixing the electrode pressing block and the support rod; the support rod is used for fixing the magnet fixing member, supporting the entire device, and limiting the distance between the two clamping flanges;

[0009] A low temperature unit, providing cooling for the viscosity measuring unit;

[0010] A temperature control unit, which keeps the viscosity measuring unit at a constant temperature;

[0011] The signal acquisition unit is used to collect the vibration signal of the metal wire, amplify and process it, and input it into the computer through the bus to regress and obtain the viscosity of the fluid.

[0012] The measuring unit comprises a high pressure chamber, a thermometer and a viscosity measuring sensor. The top flange of the high pressure chamber is provided with a chamber penetration electrode needle, which is sealed by a polytetrafluoroethylene gasket and a flange of the lower cylinder of the high pressure chamber, and can withstand a pressure of 15MPa at low temperature. The viscosity measurement sensor comprises an electrode pressing block, a metal wire, a permanent magnet, a magnet fixing part, a clamping flange and a support rod; the metal wire is a vibrating component and is located at the geometric center of the three-dimensional direction of the magnetic field generated by the permanent magnet; there are two permanent magnets, which are rectangular and arranged parallel to each other; the magnet fixing part is a cylinder with a square groove, which is used to fix the two permanent magnets on both sides of the metal wire respectively, and the permanent magnet and the magnet fixing part work together to generate a uniform constant magnetic field around the metal wire; there are a total of four electrode pressing blocks, which are used to press the two ends of the tungsten wire so that the tungsten wire has a fixed length and a constant tension, and a threaded hole is provided on the electrode pressing block, and the signal line is fixed by bolts; the clamping flange is insulated from the electrode pressing block and is used to fix the electrode pressing block and the support rod; there are two support rods, which are used to fix the magnet fixing part, support the entire device and limit the distance between the two clamping flanges; the support rod is made of the same material as the metal wire, so that when the device changes from normal temperature to a low temperature environment, the support rod and the metal wire produce the same amplitude of thermal expansion and contraction, which can ensure the constant tension of the metal wire and improve the measurement accuracy.

[0013] The cryogenic unit includes a cold source, a cooling structure and an insulating structure. The cold source includes liquid nitrogen working fluid, a liquid nitrogen container, a liquid nitrogen filling port, a liquid nitrogen level gauge, and a liquid nitrogen automatic replenishing mechanism; the cooling structure includes helium working fluid, a helium cavity, and a cooling copper plate; the insulating structure includes a vacuum interlayer outside the liquid nitrogen container, a radiation shield, and insulating foam. In terms of assembly, the innermost part of the whole device is a high-pressure cavity and a viscosity measurement sensor and fluid inside the cavity. The outside of the high-pressure cavity is covered by a helium cavity filled with helium. Outside the helium cavity is a liquid nitrogen container containing liquid nitrogen working fluid, and the liquid nitrogen container has a vacuum insulation interlayer; a copper cooling plate is arranged inside the helium cavity, which can transfer the coldness of liquid nitrogen to the cavity through metal heat conduction.

[0014] The temperature control unit includes a thermometer, an electric heater and a temperature controller. The thermometer includes a first thermometer, a second thermometer and a third thermometer. The first, second and third thermometers are respectively located at the bottom, inside and top of the high-pressure cavity. By comparing the values ​​of the three thermometers, the temperature uniformity of the device and whether it is in a steady state can be judged. The electric heater is located at the bottom of the high-pressure cavity; the leads of the thermometer and the electric heater pass through the high-pressure cavity and the helium cavity through the cabin electrode needle and the aviation connector in turn, and are connected to the temperature controller at room temperature. By adjusting the appropriate PID parameters, the temperature controller adjusts the heater power through a negative feedback algorithm, and compensates for the cold amount provided by the cold source in real time, so that the high-pressure cavity in the liquid nitrogen temperature zone is stabilized at any temperature point between 80-300K.

[0015] The signal acquisition unit includes a phase-locked amplifier, a measuring circuit and a computer. The phase-locked amplifier has the functions of outputting weak sinusoidal signals and amplifying alternating currents. The measuring circuit includes a driving current line, a high potential signal input line, a low potential signal input line and a high resistance resistor. The phase-locked amplifier provides a weak driving current to the metal wire through the driving current line. The metal wire generates a corresponding induced electromotive force when subjected to the alternating current in a uniform magnetic field. The composite electromotive force at both ends of the metal wire is input into the two input channels of the phase-locked amplifier through the high potential signal input line and the low potential signal input line, and is amplified by a differential amplifier circuit to reduce the measurement noise. After the phase-locked and orthogonal decomposition process, the phase-locked amplifier outputs four DC signals of processed amplitude, phase, sine component and cosine component, which are input into the computer through a bus.

[0016] A buffer tank is provided on the fluid pipeline connected to the measuring unit for storing the fluid being liquefied in a low-temperature environment. A thermometer and a heating wire are arranged on the buffer tank. By providing a constant power to the heating wire and observing the temperature rise rate of the thermometer, it can be determined whether the fluid in the buffer tank is in the gas phase or the liquid phase.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The core viscosity measuring element of the present invention adopts a double-end fixing method, which can effectively avoid the measurement error caused by the free torsion of the metal wire.

[0019] 2. The present invention can effectively eliminate the thermal expansion and contraction stress caused by temperature by providing two metal support frames of the same type as the vibrating metal wire, so that the resonance frequency of the metal wire remains basically constant from 80K to room temperature.

[0020] 3. The present invention uses a liquid nitrogen bath as a cold background and has a built-in thin helium interlayer with controllable cold transfer regulation, which can achieve precise temperature control as low as 80K and will not introduce factors such as vibration to affect the measurement accuracy.

[0021] 4. The present invention provides a buffer tank at the top of the high-pressure chamber, so that it has the function of determining the gas-liquid interface at low temperature.

[0022] 5. Through the above design, the present invention can operate stably under low temperature and high pressure conditions, and the viscosity error of liquid nitrogen and liquid methane measured in the liquid nitrogen temperature zone by using the above device is less than 2%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of an embodiment of the gas-liquid viscosity measurement system in the liquid nitrogen temperature range of the present invention;

[0024] Figure 2 It is a schematic diagram of the structure of the viscosity measurement unit in the present invention.

[0025] In the figure: 1-1, electrode pressing block; 1-2, metal wire; 1-3, permanent magnet; 1-4, magnet fixing member; 1-5, support rod; 1-6, clamping flange; 1-7, insulating gasket;

[0026] 2-1, liquid nitrogen container; 2-2, liquid nitrogen filling port; 2-3, liquid nitrogen level gauge; 2-4, helium chamber; 2-5, cooling copper plate; 2-6, radiation protection screen; 2-7, insulation foam; 2-8, high-pressure chamber; 2-9, electric heater; 2-10, first thermometer; 2-11, second thermometer; 2-12, third thermometer; 2-13, buffer tank; 2-14, fourth thermometer; 2-15, heating wire. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present invention. Meanwhile, it should be clear that for ease of description, the size of each part shown in the drawings is not drawn according to the actual proportional relationship.

[0030] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0031] like Figure 1 As shown, a gas-liquid viscosity measurement system suitable for helium and other cryogenic fluids, the structure of which can be summarized as a viscosity measurement unit, a cryogenic unit, a temperature control unit and a signal acquisition unit.

[0032] See also Figure 1 , Figure 1 This is a structural schematic diagram of an embodiment of the gas-liquid viscosity measurement system for the liquid nitrogen temperature range of the present invention. As shown in the figure, a gas-liquid viscosity measurement system suitable for helium and other cryogenic fluids includes: a viscosity measurement unit, a cryogenic unit, a temperature control unit and a signal acquisition unit.

[0033] The viscosity measurement unit is the core of the system, which uses electromagnetic induction and vibration principles to measure the viscosity of the fluid. Figure 1As shown, it includes: an electrode pressing block 1-1, a metal wire 1-2, a permanent magnet 1-3, a magnet fixing part 1-4, a support rod 1-5, and a clamping flange 1-6. In this embodiment, the high-pressure chamber is cylindrical, made of 316L stainless steel, and has a volume of 450mL; there are 4 electrode pressing blocks 1-1, which are used to press the two ends of the metal wire 1-2 (tungsten wire) to ensure that the tungsten wire has a fixed length and constant tension. At the same time, threaded holes are provided on the electrode pressing block 1-1 for fixing the signal line with bolts. The metal wire 1-2 is used as a vibration element, and its diameter and length are precisely designed to ensure that stable vibration can be generated when subjected to alternating current in a magnetic field. In this embodiment, the metal wire 1-2 is a tungsten wire with a radius of 0.15 mm and a length of 60 mm, which is located at the geometric center of the three-dimensional magnetic field generated by the permanent magnet 1-3; the permanent magnet 1-3 generates a uniform magnetic field, so that the metal wire generates an induced electromotive force when vibrating. In this embodiment, the permanent magnet 1-3 is two rectangular samarium cobalt magnets, and the magnetic field strength around the tungsten wire is about 0.5 T; the magnet fixing member 1-4 is a cast iron cylinder with a square groove, which is used to fix the permanent magnet 1-3 on both sides of the metal wire 1-2, with a distance of about 10 mm; the clamping flange 1-6 is insulated from the electrode block 1-1 and is used to fix the electrode block 1-1 and the support rod 1-5; there are two support rods 1-5, which are used to fix the magnet fixing 1-4, support the entire device and limit the distance between the two clamping flanges; the support rod 1-5 is made of the same material as the metal wire 1-2, so that when the device changes from normal temperature to a low temperature environment, the support rod 1-5 and the metal wire 1-2 produce the same amplitude of thermal expansion and contraction, which can ensure the constant tension of the metal wire 1-2 and improve the measurement accuracy.

[0034] In actual operation, the device needs to be fixed vertically, the tungsten wire needs to be passed through the two clamping flanges 1-6, a certain weight needs to be hung at the bottom of the metal wire 1-2, and after being left to stabilize for 24 hours, the electrode blocks 1-1 at both ends of the tungsten wire need to be fixed with bolts. When the metal wire 1-2 is subjected to an alternating current in a magnetic field, it will vibrate, and the resistance it encounters is related to the viscosity of the fluid. By measuring the induced electromotive force generated by the metal wire in the magnetic field, the viscosity of the fluid can be calculated.

[0035] The cryogenic unit provides the required cooling capacity for the viscosity measuring unit to ensure that the viscosity measurement is performed under a set low temperature environment. The cryogenic unit is mainly composed of three parts: a cold source, a cooling structure, and an insulating structure. In this embodiment, liquid nitrogen is used as a cold source and is placed in a liquid nitrogen container 2-1. Helium is placed in a helium cavity 2-4 as a cooling medium, and the helium cavity 2-4 is located between the high-pressure cavity 2-8 and the liquid nitrogen container 2-1.

[0036] The assembly process is as follows:

[0037] The innermost part is the high-pressure chamber 2-8 and the viscosity measuring sensor and fluid in the chamber. The viscosity measuring sensor is suspended in the high-pressure chamber 2-8 by a screw and is immersed in the low-temperature fluid in the chamber. The outside of the high-pressure chamber 2-8 is covered by a helium chamber 2-4 filled with helium, forming an efficient heat transfer channel. Outside the helium chamber 2-4 is a liquid nitrogen container 2-1 containing liquid nitrogen working fluid, and the liquid nitrogen container has a vacuum insulation interlayer to reduce heat transfer. A copper cold plate 2-6 is provided in the helium chamber 2-4, which can transfer the cold of liquid nitrogen to the high-pressure chamber 2-8 through metal heat conduction. The top of the helium chamber is also provided with structures such as a radiation shield 2-6 and an insulating foam 2-7 to reduce the heat leakage of the atmosphere to the device and improve the insulation effect.

[0038] The low-temperature unit provides cold energy through a cold source, transfers the cold energy to the measuring unit efficiently through a cooling structure, and reduces interference from external heat through an insulating structure, providing a stable, low-temperature measuring environment for the viscosity measuring unit, thus ensuring the accuracy and reliability of viscosity measurement.

[0039] The temperature control unit can keep the viscosity measuring unit at a constant temperature. It includes a thermometer, an electric heater 2-9 and a temperature controller. Among them, the thermometer includes a first thermometer 2-10, a second thermometer 2-11 and a third thermometer 2-12, which are respectively located at the top, inside and bottom of the high-pressure cavity, for monitoring the temperature of the high-pressure cavity, and ensuring that the degree difference of the three thermometers is within 0.5K when the device reaches a thermal equilibrium state. The second thermometer 2-11 located inside the high-pressure cavity can reflect the real temperature of the fluid. The electric heater 2-9 is located at the bottom of the high-pressure cavity and is used to provide heat to compensate for the cold provided by the cold source (such as liquid nitrogen). The heating power of the electric heater 2-9 is controlled by the temperature controller. By adjusting the appropriate PID parameters, the temperature controller adjusts the power of the heater 2-9 through a negative feedback algorithm, and compensates for the cold provided by the cold source in real time, so that the high-pressure cavity in the liquid nitrogen temperature zone is stabilized at any temperature point between 80-300K. The leads of the thermometer and electric heater pass through the high-pressure chamber and the helium chamber in turn through the cabin penetration electrode needle and the aviation connector, and are connected to the temperature controller at room temperature to ensure the reliability and safety of the leads in high-pressure and low-temperature environments.

[0040] The signal acquisition unit is used to collect the vibration signal of the metal wire 1-2. It is mainly composed of three parts: a phase-locked amplifier, a measuring circuit and a computer. The phase-locked amplifier has the function of outputting weak sinusoidal signals and amplifying alternating currents. In this system, the phase-locked amplifier outputs a driving signal to the viscosity measuring unit to provide a weak driving current for the metal wire (usually 20mV, and after passing through a 2kΩ resistor, the voltage across the metal wire is about 10μA). The metal wire 1-2 is subjected to an alternating current in a uniform magnetic field to generate a corresponding induced electromotive force. The measurement circuit includes a driving current line, a high potential signal input line, a low potential signal input line and a high resistance resistor. The composite electromotive force at both ends of the metal wire 1-2 (i.e., the sum of the induced electromotive force and the electromotive force generated by the driving current) is input into the two input channels of the phase-locked amplifier through the high potential signal input line and the low potential signal input line, and is amplified by a differential amplifier circuit to reduce the measurement noise. According to Faraday's law of electromagnetic induction and related vibration theories, the resistance to the vibration of the tungsten wire is related to the single value of the fluid viscosity, and the induced electromotive force generated by the tungsten wire in the magnetic field is proportional to the force applied to the tungsten wire. By measuring the induced electromotive force and processing it through an algorithm, the fluid viscosity can be regressed.

[0041] The buffer tank 2-13 is used to determine the liquid level in a low temperature environment. A fourth thermometer 2-14 and a heating wire 2-15 are arranged on the buffer tank 2-13. Since the thermal conductivity of liquid is much greater than that of gas, by providing a constant power to the heating wire 2-15 and observing the temperature rise rate of the thermometer, it can be determined whether the fluid in the buffer tank 2-13 is in the gas phase or the liquid phase.

[0042] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A gas-liquid viscosity measurement system suitable for helium and other cryogenic fluids, characterized in that: include: A viscosity measuring unit, used for measuring the viscosity of a fluid, comprises an electrode pressing block, a metal wire, a permanent magnet, a magnet fixing member, a support rod and a clamping flange; wherein the electrode pressing block is used for pressing the two ends of the metal wire to ensure that the metal wire has a fixed length and a constant tension; the metal wire is located in the magnetic field generated by the permanent magnet as a vibrating element; the permanent magnet is used for generating a uniform magnetic field so that the metal wire generates an induced electromotive force when vibrating; the magnet fixing member is used for fixing the permanent magnet on both sides of the metal wire; the clamping flange is insulated from the electrode pressing block and is used for fixing the electrode pressing block and the support rod; the support rod is used for fixing the magnet fixing member, supporting the entire device, and limiting the distance between the two clamping flanges; A low temperature unit, providing cooling for the viscosity measuring unit; A temperature control unit, which keeps the viscosity measuring unit at a constant temperature; The signal acquisition unit is used to collect the vibration signal of the metal wire, amplify and process it, and input it into the computer through the bus to regress and obtain the viscosity of the fluid.

2. The gas-liquid viscosity measurement system as low as liquid nitrogen temperature range according to claim 1, characterized in that: The electrode pressing block is provided with a threaded hole for fixing the signal line by bolts. The metal wire is a tungsten wire with a radius of 0.15 mm and a length of 60 mm, located at the geometric center of the three-dimensional magnetic field generated by the permanent magnet. The permanent magnet is two rectangular samarium cobalt magnets, and the magnetic field strength around the tungsten wire is about 0.5T.

3. The gas-liquid viscosity measurement system as low as liquid nitrogen temperature range according to claim 1 or 2, characterized in that: The support rod is made of the same material as the metal wire, and is used to generate the same amplitude of thermal expansion and contraction as the metal wire when the device changes from normal temperature to a low temperature environment, thereby ensuring constant tension of the metal wire.

4. The gas-liquid viscosity measurement system as low as liquid nitrogen temperature range according to claim 1, characterized in that: The low temperature unit comprises a cold source, a cold conduction structure and a heat insulation structure. The cold source comprises a liquid nitrogen working medium, a liquid nitrogen container (2-1), a liquid nitrogen filling port (2-2), a liquid nitrogen level gauge (2-3) and a liquid nitrogen automatic replenishing mechanism. The cold conduction structure comprises a helium working medium, a helium cavity (2-4) and a cold conduction copper disk (2-5). The heat insulation structure comprises a vacuum interlayer outside the liquid nitrogen container. The innermost part is a high pressure cavity (2-8) and a viscosity measuring sensor and a fluid in the cavity. The viscosity measuring sensor is connected to the high pressure cavity by a screw. The rod is suspended in a high-pressure chamber (2-8) and is immersed in the low-temperature fluid in the chamber. The outside of the high-pressure chamber (2-8) is covered by a helium chamber (2-4) filled with helium, forming an efficient heat transfer channel. The outside of the helium chamber (2-4) is a liquid nitrogen container (2-1) containing liquid nitrogen working medium. The liquid nitrogen container has a vacuum insulation interlayer to reduce heat transfer. A copper cold conduction plate (2-6) is arranged in the helium chamber (2-4) to transfer the cold of the liquid nitrogen to the high-pressure chamber (2-8) through metal heat conduction.

5. The gas-liquid viscosity measurement system as low as liquid nitrogen temperature range according to claim 4, characterized in that: The top of the helium cavity is also provided with a radiation protection screen (2-6) and heat-insulating foam (2-7) to reduce heat leakage from the atmosphere to the device and improve the heat-insulating effect.

6. The gas-liquid viscosity measurement system as low as liquid nitrogen temperature range according to claim 1, characterized in that: The temperature control unit comprises a thermometer, an electric heater (2-9) and a temperature controller; the thermometer comprises a first thermometer (2-10), a second thermometer (2-11) and a third thermometer (2-12) which are respectively located at the top, inside and bottom of the high-pressure cavity, and the temperature uniformity of the measured fluid and whether it is in a steady state can be judged by comparing the values ​​of the three thermometers; the electric heater is installed at the bottom of the high-pressure cavity to facilitate uniform distribution and compensation of heat; the heating power of the electric heater is controlled by the temperature controller, and the temperature of the high-pressure cavity is adjusted by adjusting the heating power.

7. The gas-liquid viscosity measurement system as low as liquid nitrogen temperature range according to claim 1, characterized in that: The lock-in amplifier of the signal acquisition unit is used to output a driving signal to the viscosity measurement unit, provide a weak driving current for the metal wire, and amplify the induced electromotive force generated by the metal wire in the magnetic field.

8. The gas-liquid viscosity measurement system as low as liquid nitrogen temperature range according to any one of claims 1 to 7, characterized in that: It also includes a buffer tank on the fluid pipeline connected to the viscosity measuring unit, which is used to accumulate fluid that is being liquefied in a low-temperature environment; a fourth thermometer and a heating wire are arranged on the buffer tank, and by providing a constant power to the heating wire and observing the temperature rise rate of the thermometer, it is determined whether the fluid in the buffer tank is in the gas phase or the liquid phase.

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